The present invention relates to a processing method for developing a silver halide photographic light-sensitive material which can be utilized to form a direct positive photographic image. More particularly, it relates to a method of development processing to carry out a stable processing of a direct positive type photographic light-sensitive material wherein a silver halide emulsion layer or other hydrophilic colloid layer contains a novel compound as a fogging agent with a developing solution having a pH of not less than 11.
In the field of silver halide photography, a photographic method in which a positive photographic image is obtained without using a negative image or an intermediate process producing a negative image, is called a direct positive photographic method. A photographic light-sensitive material and a photographic emulsion using such a photographic method are called a direct positive photographic light-sensitive material and a direct positive photographic emulsion, respectively.
A variety of direct positive photographic methods are known. The most useful methods are a method in which silver halide grains which have previously been fogged are exposed to light in the presence of a desensitizer followed by development, and a method comprising exposing a silver halide emulsion containing silver halide grains having light-sensitive specks mainly inside the silver halide grains to light and then developing the exposed emulsion in the presence of a fogging agent. The present invention relates to the latter method. A silver halide emulsion processing light-sensitive specks within the silver halide grains and which forms latent images mainly inside the grains is referred to as an internal latent image type silver halide emulsion, and thus are distinguished from silver halide grains which form latent images mainly on the surface of the grains.
Methods for obtaining a direct positive image by surface-developing an internal latent image type silver halide photographic emulsion in the presence of a fogging agent, and photographic emulsions and photographic light-sensitive materials employed in such methods are disclosed in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, (all of which are incorporated herein by reference to disclose such methods, emulsions, agents and materials) 2,592,250, 2,675,318, 3,227,552 and 3,761,276, British Pat. Nos. 1,011,062 and 1,151,363, Japanese Patent Publication No. 29405/68, etc.
In the internal latent image type method for obtaining a direct positive image, the fogging agent can be incorporated into a developing solution. However, by incorporating the fogging agent into the photographic emulsion layer or other layers of the photographic light-sensitive material, thereby adsorbing the fogging agent onto the surface of the silver halide grains, better reversal characteristics can be obtained.
Fogging agents which can be employed in the above-described method for obtaining a direct positive image include hydrazine and derivatives thereof as described in U.S. Pat. Nos. 2,563,785, 2,588,982 and 3,227,552, respectively. In particular, U.S. Pat. No. 3,227,552 discloses that hydrazide and hydrazine type compounds which are derivatives of hydrazine can be incorporated not only in the developing solution, but also in the light-sensitive layers.
Further, it has been proposed in U.S. Pat. No. 4,030,925 (corresponding to German Patent Application (OLS) No. 2,635,316) and U.S. Pat. No. 4,031,127 (corresponding to German Patent Application (OLS) No. 2,635,317) that acyl hydrazinophenylthiourea compounds be employed.
However, these known fogging agents are accompanied by several disadvantages, viz., they have an adverse influence on preservability of the direct positive photographic light-sensitive material, they are deficient in fogging ability for internal latent image type silver halide grains having small particle size, their reversal characteristics vary greatly depending upon changes in bromine ion concentration in the developing solution used, and their reversal characteristics vary widely depending upon changes in the amount used.
However, when an internal latent image type silver halide photographic light-sensitive material containing the above described hydrazine derivatives as a fogging agent is developed, development is not initiated without adjusting the pH of a developing solution to not less than 11.0 and as a result D max can not be obtained. This is because the fogging action of the fogging agent occurrs only when the pH is not less than 11.0. Accordingly, when a hydrazine type fogging agent is employed, it is necessary to maintain the pH of the developing solution higher than that of conventional developing solutions. However, the pH of the developing solution is varied due to aerial oxidation and the exhausted product during processing which results in the fundamental defects of changes in the photographic properties such as sensitivity, gradation, Dmax, Dmin, etc. Recently, in order to prevent the high pH developing agent from oxidation by air, some attempts have been made in which the high pH development is carried out while avoiding contact with air. For example, a method is used in which a processing solution is rendered viscous and sealed up by putting it into a pod. Processing is then carried out by mechanically rupturing the pod just before development. In accordance with another method a developing solution is put into a sealed container and the developing solution is sprayed on the photographic light-sensitive material using a spray method. However, these methods have disadvantages such as they are not capable of processing as large an area as a dip type processing system. Furthermore, the mechanism of the processing machine becomes complicated. Therefore, these methods are not suitable for practical use. Accordingly, it is desirable to develope a processing method which is stable even at a high pH and which can be applicable to conventional dip type processing machines.
When a silver halide photographic light-sensitive material is processed, the pH of the processing solution decreases, the amount of halogen increases and the developing agent and sulfurous acid are consumed. Processing solutions of this type are called exhausted processing solutions. Photographic light-sensitive materials containing a fogging agent are particularly susceptible to a change in pH and the sensitivity and Dmax thereof are remarkably affected. Sodium carbonate or trisodium phosphate is conventionally used as a buffer in connection with such processing solutions. However, these buffers are not desirable because they are only effective at a pH of up to about 10 and have no buffering function at a pH of about 11 and 12.